Past exam of the MPhil in micro- and nanotechnology enterprise course of the University of Cambridge / 2023 / Paper 2 / Section A(iii) / 18 / iii / Solution

Reading the lowest point of the order-disorder boundary in the supplied experimental diagram gives approximately(about $0.45$–$0.47$, allowing for the graphical resolution). The ordered region just above that minimum is lamellar.

This is a reading of the supplied polyisoprene-polystyrene phase diagram. It should not be replaced by the often quoted symmetric-chain mean-field theory value $10.5$: that refers to a different idealization and is not the minimum drawn here.